a) Field of the Invention
This invention relates to a gas generating device for actuating a safety apparatus such as an air bag system or a webbing pretensioner of a seat belt system, for example, in the event of an emergency such as a collision of an automotive vehicle so that an occupant can be protected. More specifically, this invention is concerned with a gas generating device which has been improved to minimize leakage of high-temperature and high-pressure gas after firing of a detonator and also to avoid accidental actuation in the course of its assembling or mounting work.
b) Description of the Related Art
An air bag system and/or a webbing pretensioner has been used to protect an occupant in the event of an emergency such as a collision of an automotive vehicle. It is necessary to make these devices actuate instantaneously at the time of a collision, so that a gas generating device is employed to cause explosive combustion of a gas generating chemical reagent such as explosive for the generation of high-pressure gas.
These gas generating devices are available in two types, one being electrically fired and the other mechanically fired. Mechanical devices are however finding increasing popularity in recent years for their simpler construction and lower price.
As such a mechanical gas generating device, the gas generating device disclosed in Japanese Patent Application Laid-Open (Kokai) No. HEI 3-132447 is known. This mechanical gas generating device is provided with a small-diameter hole between a detonator and a gas-generating chemical reagent so that, after the detonator is struck, a flame from the detonator can be surely guided into a compartment with the gas-generating chemical reagent filled therein and the high-temperature and high-pressure gas produced from the gas-generating chemical reagent can be prevented from flowing backward to a side of the detonator. To ensure guidance of a flame, the small-diameter hole is defined to have a diameter of at least 0.5 mm and an overall length not greater than 8 times the diameter. To prevent a backward flow of high-temperature and high-pressure gas, on the other hand, the small-diameter hole is defined to have a diameter not greater than 1.2 mm and an overall length at least 5 times as great as the diameter. Namely, the diameter is in a range of from 0.5 mm to 1.2 mm while the overall length is in a range of from 5 to 8 times as great as the diameter.
For the provision of the small-diameter hole between the detonator and the gas-generating chemical reagent, the above-described mechanical gas generating device is accompanied by the following problems:
1) High-temperature and high-pressure gas from the detonator is substantially blocked by the small-diameter hole. Accordingly, the high-temperature and high-pressure gas produced from an explosive used in the detonator cannot be used effectively as webbing-winding power so that the gas-generating chemical reagent is required in a large quantity. PA0 2) The high-temperature and high-pressure gas from the detonator leaks to a side of a hammer pin trigger device. It is therefore necessary to construct the hammer pin trigger device strong enough to withstand the pressure of the gas. For example, substantially strength is required for a casing which accommodates the hammer pin trigger device. PA0 3) The gas generating device unavoidably becomes longer because of the need for the provision of the small-diameter hole inside the gas generating device. PA0 1) In addition to high-temperature and high-pressure gas produced from the gas-generating chemical reagent, high-temperature and high-pressure gas from the detonator can also be used effectively as webbing-winding power. The quantity of the gas-generating chemical reagent can therefore be reduced. PA0 2) The hammer pin trigger device is protected from the high-temperature and high-pressure gas produced by the gas-generating chemical reagent and the detonator, because the high-temperature and high-pressure gas is prevented from leaking to the side of the hammer pin trigger device. This has made it possible to use a light-weight material such as a resin for a casing of the hammer pin trigger device. PA0 3) The hammer pin insertion hole is located outside the gas generator, thereby making it possible to form the gas generator short or small. This means that the gas generator can be manufactured at lower cost. As the gas generator accounts for a substantial part of the overall manufacturing cost of the gas generating device, the reduction in the manufacturing cost of the gas generator can make a significant contribution for a reduction in the manufacturing cost of the gas generating device.
Referring now to FIGS. 3 and 4, a description will hereinafter be made of a further example of conventional gas generating devices.
FIG. 3 is a cross-sectional view of the conventional gas generating device as applied to the webbing pretensioner, and FIG. 4 is a cross-sectional view illustrating a problem inherent to the conventional gas generating device.
As is illustrated in FIG. 3, a frame 1 of a webbing retractor (not shown) for an unillustrated automotive vehicle, said frame having been formed by bending a steel plate, has a bracket 2 for mounting a gas generating device 90 on the webbing retractor. A pretensioner 10 and a hammer pin trigger device 20 are arranged on left-hand and right-hand side walls of the bracket 2 as viewed in the figure. The pretensioner 10 and the hammer pin trigger device 20 are fixed together by bolts 29, with the bracket 2 being held therebetween.
The pretensioner 10 is equipped with a substantially cylindrical housing 11 fixed on the bracket 2 and a cylinder 13 threadedly secured in an end portion of the housing 11 and extending upwardly. A gas compartment 12 inside the housing 11 and a chamber 14 inside the cylinder 13 are in mutual communication, and a piston 15 is slidably fitted in the cylinder 13. A wire cable 16 which is wound on a take-up spindle of the unillustrated webbing retractor is connected at a free end thereof to the piston 15.
A gas generator 30 is accommodated in an end portion of the housing 11, said end portion being on a side of the bracket 2. This gas generator 30 has a stepped, bottom-closed cylindrical casing 31, a gas generating chemical reagent 32 sealed in the casing 31, and a detonator 33 for firing the gas generating chemical reagent 32. The gas generator 30 is in threaded engagement with the housing 11 and, by a cover 37 substantially closing up a bracket-side opening of the housing 11, is held within the housing 11.
The hammer pin trigger device 20 has, as is depicted in FIG. 3, a bottom-closed cylindrical housing member 21 mounted on the bracket 2, an unillustrated hammer pin trigger mechanism equipped with an inertia member (not shown) accommodated within the housing member 21 for displacement upon application of a deceleration of at least a predetermined value thereon in the event of a collision, a hammer pin 27 disposed displaceably by the hammer pin trigger mechanism, a spacer 26 made of a metal or resin and defining a through-hole in which the hammer pin 27 is slidably and supportedly fitted, and a hammer pin side cover 25 disposed in an opening of the housing member 21 and covering and holding the hammer pin trigger mechanism and the spacer 26 within the housing member 21.
Operation of the above-described webbing pretensioner will next be described. Upon application of a deceleration of at least a predetermined value on the hammer pin trigger device 20 by a collision of an automotive vehicle or a like cause, the unillustrated inertia member causes the hammer pin 27 to displace so that the hammer pin 27 strikes the detonator 33. The detonator 33 so struck by the hammer pin 27 is ignited to fire the gas generating chemical reagent 32 arranged adjacent the detonator 33. The gas generating chemical reagent 32 so fired burns explosively, resulting in production of a large amount of high-temperature and high-pressure gas. This high-temperature gas instantaneously spreads from the gas compartment 12 inside the housing 11 of the pretensioner 10 to the chamber 14 inside the cylinder 13 so that the gas compartment 12 and the chamber 14 are filled up with the gas. As a consequence, the piston 15 is caused to abruptly move upwards within the cylinder 13 by a thrust of the expanding pressure of the gas, so that the wire cable 16 is pulled. As a result, the unillustrated take-up spindle around which the wire cable 16 is wound is caused to rotate in a webbing winding direction, whereby any slack in a webbing is taken up.
Incidentally, the hammer pin 27 in the conventional gas generating device 90 has, as is shown in FIG. 3, a uniform diameter except that a free end portion thereof which strikes the detonator 33 is pointed and a longitudinal central portion thereof carries an upright flange against which the unillustrated inertia member collides.
Further, the inner diameter D1 (see FIG. 4) of a hammer pin insertion hole 38 formed in the cover 37 is set substantially larger than the outer diameter of the hammer pin 27 so that any misalignment between an axis of the hammer pin trigger device 20 and that of the gas generator 30 can be tolerated to avoid contact between the hammer pin 27 and a wall of the hammer pin insertion hole 38 and hence any loss in detonator-striking energy.
In the course of the assembly of the conventional gas generating device 90, specifically at the time point that the gas generator 30 has been held in place by the cover 37 subsequent to its placement inside the housing 11 as shown in FIG. 4, the detonator 33 is exposed to the outside through the hammer pin insertion hole 38 formed in the cover 37 and having the large inner diameter.
If a worker should accidentally insert a self-tapping screw 39 or the like, which is employed for the assembly of the gas generating device 90 or for the mounting of the gas generating device 90 on the unillustrated webbing retractor, into the hammer pin insertion hole 38 and should then strike the detonator 33, the gas generator 30 is triggered to blow out high-temperature and high-pressure gas. This is certainly very dangerous to the worker. The conventional gas generating device 90 is therefore accompanied by the above-described potential problem. As the hammer pin insertion hole 38 is large in this conventional example, the conventional gas generating device 90 also involves the problem that, after the detonator 33 is fired, the resulting high-temperature and high-pressure gas may leak out of the hammer pin insertion hole 38.